Neospora is a pathogenic protozoan parasite of animals which has recently been recognized as a major cause of abortion, neonatal death, congenital infection, and encephalitic disease in mammals. Dubey and Lindsay, 1993, Parasitology Today, 9:452–458. N. caninum infects dogs, and congenitally infects pups, often leading to paralysis. Tachyzoites of N. caninum have been isolated from naturally infected pups. Lindsay and Dubey, 1989, J. Parasitol. 75:163–165. Neospora spp. are a major cause of abortion in dairy cattle. Cases of Neospora-related disease, i.e., neosporosis, have also been reported in goats, sheep and horses.
Although N. caninum is superficially similar to the pathogen, Toxoplasma gondii, N. caninum and T. gondii have been distinguished from each other antigenically and ultrastructurally. Dubey and Lindsay, 1993, above. In addition, Neospora-like protozoal parasites isolated from the brains of aborted bovine fetuses and continuously cultured in vitro were shown to be antigenically and ultrastructurally distinct from both T. gondii and Hammondia hammondi, and most similar to N. caninum. Conrad et al., 1993, Parasitology 106:239–249. Furthermore, analysis of nuclear small subunit ribosomal RNA genes revealed no nucleotide differences between Neospora spp. isolated from cattle and dogs, but showed consistent differences from T. gondii. Marsh et al., 1995, J. Parasitol. 81:530–535.
The etiologic role of a bovine isolate of Neospora in bovine abortion and congenital disease has been confirmed. Barr et al., 1994, J. Vet. Diag. Invest. 6:207–215. A rodent model of central nervous system neosporosis has been developed using inbred BALB/c mice infected with N. caninum. Lindsay et al., 1995, J. Parasitol. 81:313–315. In addition, models to study transplacental transmission of N. caninum in pregnant outbred and inbred mice have been described by Cole et al., 1995, J. Parasiol. 81:730–732, and by Long et al., 1996, J. Parasitol. 82:608–611, respectively. Furthermore, an experimental N. caninum pygmy goat model that closely resembles naturally acquired Neospora-induced cattle abortion has been demonstrated. Lindsay et al., 1995, Am. J. Vet. Res. 56:1176–1180.
WO 9525541 discloses a biologically pure culture of bovine Neospora, methods of detecting anti-Neospora antibodies and Neospora-specific nucleic acids, and a composition containing a bovine Neospora antigen and carrier for use as a vaccine. WO 9525541 does not, however, teach attenuated live cultures of Neospora, or live vaccines prepared therefrom which are able to trigger a protective immune response in a vaccinated animal.